USB on-the-go full-speed (OTG_FS) RM0033
968/1381 RM0033 Rev 9
the 5 V V
BUS
line. The external charge pump can be driven by any GPIO output. This is
required for the OTG A-host, A-device and host-only configurations.
The V
BUS
input ensures that valid V
BUS
levels are supplied by the charge pump during USB
operations while the charge pump overcurrent output can be input to any GPIO pin
configured to generate port interrupts. The overcurrent ISR must promptly disable the V
BUS
generation.
The V
BUS
pin can be freed by disabling the V
BUS
sensing option. This is done by setting the
NOVBUSSENS bit in the OTG_FS_GCCFG register. In this case the V
BUS
is considered
internally to be always at V
BUS
valid level (5 V).
Figure 352. USB host-only connection
1. STMPS2141STR needed only if the application has to support a V
BUS
powered device. A basic power
switch can be used if 5 V are available on the application board.
2. V
DD
range is between 2 V and 3.6 V.
29.6.1 SRP-capable host
SRP support is available through the SRP capable bit in the global USB configuration
register (SRPCAP bit in OTG_FS_GUSBCFG). With the SRP feature enabled, the host can
save power by switching off the V
BUS
power while the USB session is suspended.
The SRP host mode program model is described in detail in the A-device session request
protocol section.
29.6.2 USB host states
Host port power
On-chip 5 V V
BUS
generation is not supported. For this reason, a charge pump or, if 5 V are
available on the application board, a basic power switch, must be added externally to drive
the 5 V V
BUS
line. The external charge pump can be driven by any GPIO output. When the
application decides to power on V
BUS
using the chosen GPIO, it must also set the port
power bit in the host port control and status register (PPWR bit in OTG_FS_HPRT).
MSv36915V2
STMPS2141STR
Current-limited
power distribution
switch
(2)
OSC_IN
OSC_OUT
GPIO
GPIO + IRQ
EN
Overcurrent
5 V
5 V Pwr
VBUS
DM
DP
V
SS
USB Std-A connector
V
DD
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